The present invention relates to the field of high thermal conductivity pastes which are used as a heat transfer means for cooling electronic components and, in particular, relates to a high thermal conductivity paste which is useful in cooling under low temperature conditions.
Electronic components generate heat and in many applications the heat needs to be effectively dissipated for the device to function properly. In electronic components such as semiconductor devices and the like, the need to achieve greater computer speeds and the miniaturization of electronic components has resulted in electronic components which generate more heat. The use of such electronic components is only practicable, however, when the heat generated is effectively removed from the active components and a number of techniques have been developed to cool such electronic components.
Various systems have been disclosed in the art for providing a separate cooling member to cool the electronic component. Fins, channels, baffles, caps and other heat exchanger type devices have been developed to remove heat from the electronic component. In some cases, the electronic component, and perhaps other portions of the overall electronic assembly as well, are refrigerated to below room temperature in an effort to more effectively cool the electronic component.
In most of these cooling devices there is an air space between the electronic component to be cooled and the cooling device which air space has a relatively low heat transfer rate. To overcome this problem, thermal compounds commonly referred to as thermal greases or thermal pastes (hereafter collectively referred to as thermal pastes) have been developed to enhance the transfer of heat from the electronic component to the cooling device by contacting and connecting both surfaces and providing a high heat transfer conducting means. The thermal paste must have high thermal conductivity and preferably be an electrical insulator. The paste must also have a low viscosity and be compliant so that the thermal paste can be easily applied to the surfaces of the electronic component to be cooled and can conform with the microscopically rough surface of the electronic component which are often bowed or tilted to minimize air gaps which are detrimental to the cooling process. Low viscosity is also important because the electronic components are fragile and the force needed to apply the thermal paste must be minimal. It is a further requirement that the thermal paste be able to withstand power cycling and the mechanical stresses arising from the differences in coefficient of thermal expansion of the electronic component, thermal paste and cooling system over the life of the component without the thermal paste degrading significantly in thermal conductivity or mechanically, such as experiencing phase separation between the liquid and solid components of the thermal paste.
A number of thermal pastes have been developed to be used in electronic systems and, in general, the thermal paste comprises thermally conductive filler particles and a dispersant in a liquid dielectric carrier.
Iruvanti et al. U.S. Pat. No. 5,098,609, the disclosure of which is incorporated by reference herein, discloses stable high solids, high thermal conductivity thermal pastes which contain a stabilizing dispersant to inhibit liquid-solid separation and which facilitate incorporation of more solid fillers into the paste. The liquid dielectric carrier is selected from paraffinic hydrocarbons, such as mineral oil, silicone oils, mixtures of glycerides, halogenated hydrocarbons, olefinic hydrocarbons, aromatic hydrocarbons and mixtures of two or more of the above carriers.
Iruvanti et al. U.S. Pat. No. 5,591,789, the disclosure of which is incorporated by reference herein, discloses a high thermal conductivity paste having a polyester dispersant. The liquid dielectric carrier is a poly(alpha-olefin) oil.
In certain cooling applications where the electronic component is refrigerated or otherwise cooled in some manner, it is still necessary to be able to efficiently remove heat from the electronic component. Accordingly, thermal pastes are desirable even in low temperature applications (e.g., room temperature to xe2x88x9230xc2x0). However, none of the thermal pastes disclosed in the above references are suitable for low temperature applications because the pastes become too hard.
It would be desirable to have a thermal paste that remains soft and sticky under low temperature conditions.
Accordingly, it is a purpose of the present invention to have a thermal paste that remains soft and sticky under low temperature conditions.
It is another purpose of the present invention to have a thermal paste for low temperature conditions that is easily manufactured from commercially available components.
Another aspect of the invention is to provide a thermal paste that can be easily cleaned with common solvents to enable rework of electronic components. Thermal pastes or greases made with silicone oil generally are difficult to clean, and often require environmentally unacceptable solvents such as methylene chloride.
Accordingly, it is yet another purpose of the present invention to have a thermal paste that can be easily cleaned with common solvents to enable rework of electronic components.
These and other purposes of the present invention will become more apparent after referring to the following invention considered in conjunction with the accompanying drawings.
The purposes of the invention have been achieved by providing, according to a first aspect of the present invention, a thermal paste for low temperature applications comprising:
a thermally conducting solid filler;
a dispersant; and
a linear alkylbenzene liquid carrier.
According to a second aspect of the present invention, there is provided a method for increasing the cooling of an electronic component by the use of a cooling member proximate to the electronic component comprising the step of:
applying a thermal paste to the surface of the electronic component and the cooling member, the thermal paste comprising a thermally conducting solid filler, a dispersant, and a linear alkylbenzene liquid carrier.